1. Field of the Invention
This invention relates to motor vehicle suspensions. More particularly, the invention relates to lift mechanisms for retractable suspensions used on trailers which are adaptable for both highway and railroad use.
2. Scope of the Prior Art
An increasingly common form of transportation includes the use of trailers which are adapted for both highway and railroad use. Such trailers are typically constructed with reinforced frames designed to withstand the forces of normal rail service as well as the forces associated with normal highway service. The wheel gear upon which the trailers ride obviously depends upon whether the trailer is to be used in normal highway service or on a railroad track. In the former, conventional ground-engaging rubber tires are required, and in the latter, a rail wheel set must be used, sometimes known as a rail bogie.
One trailer in common use is known as a Mark IV trailer which is a completely integrated intermodal vehicle. The Mark IV trailer comprises a two-axle highway wheel set and a single axle rail wheel set, both of which are retractable by means of an air suspension. In the highway mode, the rail wheel set is retracted, and in the rail mode, the highway wheel set is retracted. Typically, the rail wheels are disposed between the tandem axles of the highway wheels. One of the problems with the Mark IV design is that the trailer carries an extra load of deadweight which necessarily forces restrictions on the load-carrying capacity of the trailer in highway use.
Another version commonly used is known as a Mark V trailer which carries no rail-running gear. Instead, its highway wheel set slides forward so that the trailer can be mounted on a freestanding, air suspension, two-axle rail bogie. The suspension in the highway wheel set of the Mark V trailer provides multiple functions. Not only does it provide a normal highway suspension for the wheel set, but it also enables the rear of the trailer to lift relative to the ground to permit the rail bogie to be maneuvered into place underneath the rear of the trailer. The suspension also retracts the highway wheel set relative to the ground so that the trailer comes to rest upon the rail bogie, thus permitting the trailer to be utilized in normal rail service.
Both systems provide lift mechanisms for retracting the highway wheel set with respect to the trailer. The Mark V trailer is lighter than the Mark IV because it does not carry the extra deadweight. However, both trailers provide limited lift of the highway wheel set so that there is a low clearance when the trailer is in the rail mode. Further, the lift mechanisms in both trailers are biased toward the retracted position to prevent the unused wheel set from accidentally falling and interfering with the action of the used wheel set.
There is a need to provide additional lift to a highway wheel set in a trailer that is adapted for use with a detachable rail bogie. It has also been found advantageous to provide an alternative means for securing the highway wheel set in the retracted position.